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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 21 |
| 4 | 81 |
| 5 | 316 |
| 6 | 1290 |
| 7 | 5364 |
| 8 | 22671 |
| 9 | 97134 |
| 10 | 421395 |
| 11 | 1842859 |
| 12 | 8120955 |
| 13 | 36030211 |
| 14 | 160720110 |
| 15 | 720399057 |
| 16 | 3243337538 |
| 17 | 14657442438 |
| 18 | 66462177523 |
| 19 | 302297076810 |
| 20 | 1378768346987 |
| 21 | 6304196472379 |
| 22 | 28891248763767 |
| 23 | 132683418962429 |
| 24 | 610521419414194 |
| 25 | 2814224144808525 |
| 26 | 12993729376334312 |
| 27 | 60085936281977584 |
[1,2,6,21,81,316,1290,5364,22671,97134,421395, 1842859,8120955,36030211,160720110,720399057, 3243337538,14657442438,66462177523,302297076810, 1378768346987,6304196472379,28891248763767, 132683418962429,610521419414194,2814224144808525, 12993729376334312,60085936281977584] |